Novel designs for an electric warming blanket including a flexible heater

ABSTRACT

An electric warming blanket includes a flexible heater that may be enclosed within a flexible shell, which is, preferably, water resistant and may extend beyond lateral edges of the heater to support stiffening members. A layer of non-conductive flexible porous material may be bonded to one or both sides of the heater. When the heater is enclosed in the shell, a layer of thermal insulation may be disposed between one side of the heater and the shell. A temperature sensor may be coupled to the heater at a location where the heater will be in conductive contact with a body when the blanket is draped thereover, and at least one super-over temperature sensor may also be coupled to the heater; the at least one super over-temperature sensor is adapted to interrupt a supply of power to the heater.

PRIORITY CLAIM

The present application claims priority to co-pending provisional applications Ser. No. 60/825,573, entitled HEATING BLANKET SYSTEM filed on Sep. 13, 2006; Ser. No. 60/722,106, entitled ELECTRIC WARMING BLANKET INCLUDING TEMPERATURE ZONES AUTOMATICALLY OPTIMIZED, filed Sep. 29, 2005; and Ser. No. 60/722,246, entitled HEATING BLANKET, filed Sep. 29, 2005; all of which are incorporated by reference in their entireties herein.

RELATED APPLICATIONS

The present application is related to the following commonly assigned utility patent applications, all of which are filed concurrently herewith and all of which are hereby incorporated by reference in their entireties: A) ELECTRIC WARMING BLANKET HAVING OPTIMIZED TEMPERATURE ZONES, Practitioner docket number 49278.2.5.2; B) NOVEL DESIGNS FOR HEATING BLANKETS AND PADS, Practitioner docket number 49278.2.7.2; C) TEMPERATURE SENSOR ASSEMBLIES FOR ELECTRIC WARMING BLANKETS, Practitioner docket number 49278.2.9.2; D) BUS BAR ATTACHMENTS FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.16; and E) BUS BAR INTERFACES FOR FLEXIBLE HEATING ELEMENTS, Practitioner docket number 49278.2.17.

TECHNICAL FIELD

The present invention is related to electric heating or warming blankets or pads and more particularly to those including flexible heating elements.

BACKGROUND

It is well established that surgical patients under anesthesia become poikilothermic. This means that the patients lose their ability to control their body temperature and will take on or lose heat depending on the temperature of the environment. Since modern operating rooms are all air conditioned to a relatively low temperature for surgeon comfort, the majority of patients undergoing general anesthesia will lose heat and become clinically hypothermic if not warmed.

Over the past 15 years, forced-air warming (FAW) has become the “standard of care” for preventing and treating the hypothermia caused by anesthesia and surgery. FAW consists of a large heater/blower attached by a hose to an inflatable air blanket. The warm air is distributed over the patient within the chambers of the blanket and then is exhausted onto the patient through holes in the bottom surface of the blanket.

Although FAW is clinically effective, it suffers from several problems including: a relatively high price; air blowing in the operating room, which can be noisy and can potentially contaminate the surgical field; and bulkiness, which, at times, may obscure the view of the surgeon. Moreover, the low specific heat of air and the rapid loss of heat from air require that the temperature of the air, as it leaves the hose, be dangerously high—in some products as high as 45° C. This poses significant dangers for the patient. Second and third degree burns have occurred both because of contact between the hose and the patient's skin, and by blowing hot air directly from the hose onto the skin without connecting a blanket to the hose. This condition is common enough to have its own name—“hosing.” The manufacturers of forced air warming equipment actively warn their users against hosing and the risks it poses to the patient.

Electric warming blankets overcome the aforementioned problems with FAW. Some of these warming blankets employ flexible heaters, which may be prone to potentially dangerous conditions, for example, when the blankets, including the flexible heaters, are folded over onto themselves. Such folding, which is sometimes called “rucking”, may result in electrical shorting between portions of the flexible heater. The short circuit becomes a relatively low-resistance pathway and current will preferentially flow through the low resistance area. The increased current flow may cause that area to get very hot which may cause a burn risk to the patient.

Electrical shorting with such heaters has been addressed by electrically insulating the heater by laminating a relatively thick layer of plastic film to each side of the heater. However, when electrical insulation is accomplished by laminating a relatively thick layer of plastic film to each side of the fabric heater, the resulting laminated structure becomes relatively stiff and non-flexible and does not exhibit desirable draping characteristics. A non-flexible, non-draping blanket is not only uncomfortable for the patient, but is also thermally inefficient because of the poor thermal contact with the patient. Non-flexible thermal blankets can also apply excessive heat and pressure to patient “high spots,” such as boney prominences.

Further, rucking may cause overheating of the flexible heater due to added thermal insulation over the side of the heater that is beneath a folded-over portion of the heater. Normally, the heater will lose heat off of both surfaces simultaneously. If the heater is folded back on itself, the upper layer of heater becomes a very effective guard heater. This near perfect thermal insulation on the upper side prevents the lower layer (e.g., the patient side) from losing heat to the environment. Therefore, the temperature of the lower of the two layers will increase to a new and higher equilibrium temperature. If the heater is folded like a “Z” so that there is an area that is three layers thick, the middle layer of the “Z” will not be able to lose heat from either of its surfaces. The area in the middle of the three-layer fold will significantly over-heat and may become unsafe.

A traditional approach to avoiding electrical shorting and/or overheating has been to purposefully make the blanket relatively stiff in order to prevent rucking. This stiffening is typically accomplished by laminating the heater material to plastic film or enclosing the heater in a relatively stiff outer cover. As previously discussed, stiff blankets may be uncomfortable for a patient and may be less efficient in heating the patient, since the stiffness prevents a draping of the blankets over the patient to maximize an area of the patient's skin receiving conductive as well as radiant heat transfer.

Accordingly, there is a need for a blanket that can avoid electrical shorting and/or overheating caused by rucking without becoming so stiff as to lose desirable draping characteristics. Various embodiments of the invention described herein solve one or more of the problems discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of the present invention and therefore do not limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description. Embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like numerals denote like elements.

FIG. 1A is a plan view of a flexible heating blanket subassembly for a heating blanket, according to some embodiments of the present invention.

FIGS. 1B-C are end views of two embodiments of the subassembly shown in FIG. 1A.

FIG. 1D is a schematic showing a blanket including the subassembly of FIG. 1A draped over a body.

FIG. 2A is a top plan view of a heating element assembly, according to some embodiments of the present invention, which may be incorporated in the blanket shown in FIG. 3A.

FIG. 2B is a section view through section line A-A of FIG. 2A.

FIG. 2C is an enlarged plan view and corresponding end view schematic of a portion of the assembly shown in FIG. 2A, according to some embodiments of the present invention.

FIG. 2D is an enlarged view of a portion of the assembly shown in FIG. 2A, according to some embodiments of the present invention.

FIG. 3A is a top plan view, including partial cut-away views, of a lower body heating blanket, according to some embodiments of the present invention.

FIG. 3B is a schematic side view of the blanket of FIG. 3A draped over a lower body portion of a patient.

FIG. 3C is a top plan view of a heating element assembly, which may be incorporated in the blanket shown in FIG. 3A.

FIG. 3D is an cross-section view through section line D-D of FIG. 3C.

FIG. 4A is a plan view of flexible heating element, according to some alternate embodiments of the present invention.

FIG. 4B is a top plan view, including a partial cut-away view, of a heating element assembly, according to some embodiments of the present invention, which may be incorporated in the blanket shown in FIG. 4C.

FIG. 4C is a top plan view, including a partial cut-away view, of an upper body heating blanket, according to some embodiments of the present invention.

FIG. 4D is a schematic end view of the blanket of FIG. 4B draped over an upper body portion of a patient.

DETAILED DESCRIPTION

The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides practical illustrations for implementing exemplary embodiments of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of skill in the field of the invention. Those skilled in the art will recognize that many of the examples provided have suitable alternatives that can be utilized. The term ‘blanket’, used to describe embodiments of the present invention, may be considered to encompass heating blankets and pads.

FIG. 1A is a plan view of a flexible heating blanket subassembly 100, according to some embodiments of the present invention; and FOGS. 1B-C are end views of two embodiments of the subassembly shown in FIG. 1A. FIG. 1A illustrates a flexible sheet-like heating element or heater 10 of subassembly 100 including a first end 101, a second end 102, a first lateral portion 11 extending between ends 101, 102, and a second lateral portion 12, opposite first lateral portion 11, also extending between ends 101, 102. According to preferred embodiments of the present invention, heating element 10 comprises a conductive fabric or a fabric incorporating closely spaced conductive elements such that heater 10 has a substantially uniform watt density output, preferably less than approximately 0.5 watts/sq. inch, and more preferably between approximately 0.2 and approximately 0.4 watts/sq. inch, across a surface area, of one or both sides 13, 14 (FIGS. 1B-C), the surface area including and extending between lateral portions 11, 12 of heater 10. Some examples of conductive fabrics which may be employed by embodiments of the present invention include, without limitation, carbon fiber fabrics, fabrics made from carbonized fibers, woven or non-woven non-conductive substrates coated with a conductive material, for example, polypyrrole, carbonized ink, or metalized ink.

FIG. 1A further illustrates subassembly 100 including two bus bars 15 coupled to heater 10 for powering heater 10; each bar 15 is shown extending alongside opposing lateral portions 11, 12, between first and second ends 101, 102. With reference to FIG. 1B, according to some embodiments, bus bars 15 are coupled to heating element 10 within folds of opposing wrapped perimeter edges 108 of heater 10 by a stitched coupling 145, for example, formed with conductive thread such as silver-coated polyester or nylon thread (Marktek Inc., Chesterfield, Mo.), extending through edges 108 of heater 10, bars 15, and again through heater 10 on opposite side of bars 15. According to alternate embodiments heater 10 is not folded over bus bars 15 as shown. Alternative threads or yarns employed by embodiments of the present invention may be made of other polymeric or natural fibers coated with other electrically conductive materials; in addition, nickel, gold, platinum and various conductive polymers can be used to make conductive threads. Metal threads such as stainless steel, copper or nickel could also be used for this application. According to an exemplary embodiment, bars 15 are comprised of flattened tubes of braided wires, such as are known to those skilled in the art, for example, a flat braided silver coated copper wire, and may thus accommodate the thread extending therethrough, passing through openings between the braided wires thereof. In addition such bars are flexible to enhance the flexibility of blanket subassembly 100. According to alternate embodiments, bus bars 15 can be a conductive foil or wire, flattened braided wires not formed in tubes, an embroidery of conductive thread, or a printing of conductive ink. Preferably, bus bars 15 are each a flat braided silver-coated copper wire material, since a silver coating has shown superior durability with repeated flexion, as compared to tin-coated wire, for example, and may be less susceptible to oxidative interaction with a polypyrrole coating of heater 10 according to an embodiment described below. Additionally, an oxidative potential, related to dissimilar metals in contact with one another is reduced if a silver-coated thread is used for stitched coupling 145 of a silver-coated bus bar 15.

According to an exemplary embodiment, a conductive fabric comprising heating element 10 comprises a non-woven polyester having a basis weight of approximately 130 g/m² and being 100% coated with polypyrrole (available from Eeonyx Inc., Pinole, Calif.); the coated fabric has an average resistance, for example, determined with a four point probe measurement, of approximately 15-20 ohms per square inch at about 48 volts, which is suitable to produce the preferred watt density of 0.2 to 0.4 watts/sq. in. for surface areas of heating element 10 having a width, between bus bars 15, in the neighborhood of about 20 inches. Such a width is suitable for a lower body heating blanket, some embodiments of which will be described below. A resistance of such a conductive fabric may be tailored for different widths between bus bars (wider requiring a lower resistance and narrower requiring a higher resistance) by increasing or decreasing a surface area of the fabric that can receive the conductive coating, for example by increasing or decreasing the basis weight of the fabric. Resistance over the surface area of the conductive fabrics is generally uniform in many embodiments of the present invention. However, the resistance over different portions of the surface area of conductive fabrics such as these may vary, for example, due to variation in a thickness of a conductive coating, variation within the conductive coating itself, variation in effective surface area of the substrate which is available to receive the conductive coating, or variation in the density of the substrate itself. Local surface resistance across a heating element, for example element 10, is directly related to heat generation according to the following relationship: Q(Joules)=I ²(Amps)×R(Ohms) Variability in resistance thus translates into variability in heat generation, which is measured as a temperature. According to preferred embodiments of the present invention, which are employed to warm patients undergoing surgery, precise temperature control is desirable. Means for determining heating element temperatures, which average out temperature variability caused by resistance variability across a surface of the heating element, are described below in conjunction with FIGS. 2A-B.

A flexibility of blanket subassembly 100, provided primarily by flexible heating element 10, and optionally enhanced by the incorporation of flexible bus bars, allows blanket subassembly 100 to conform to the contours of a body, for example, all or a portion of a patient undergoing surgery, rather than simply bridging across high spots of the body; such conformance may optimize a conductive heat transfer from element 10 to a surface of the body. However, as illustrated in FIG. 1D, heating element 10 may be draped over a body 16 such that lateral portions 11, 12 do not contact side surfaces of body 16; the mechanism of heat transfer between portions 11, 12 and body 16, as illustrated in FIG. 1D, is primarily radiant with some convection.

The uniform watt-density output across the surface areas of preferred embodiments of heating element 10 translates into generally uniform heating of the surface areas, but not necessarily a uniform temperature. At locations of heating element 10 which are in conductive contact with a body acting as a heat sink, for example, body 16, the heat is efficiently drawn away from heating element 10 and into the body, for example by blood flow, while at those locations where element 10 does not come into conductive contact with the body, for example lateral portions 11, 12 as illustrated in FIG. 1D, an insulating air gap exists between the body and those portions, so that the heat is not drawn off those portions as easily. Therefore, those portions of heating element 10 not in conductive contact with the body will gain in temperature, since heat is not transferred as efficiently from these portions as from those in conductive contact with the body. The ‘non-contacting’ portions will reach a higher equilibrium temperature than that of the ‘contacting’ portions, when the radiant and convective heat loss equal the constant heat production through heating element 10. Although radiant and convective heat transfer are more efficient at higher heater temperatures, the laws of thermodynamics dictate that as long as there is a uniform watt-density of heat production, even at the higher temperature, the radiant and convective heat transfer from a blanket of this construction will result in a lower heat flux to the skin than the heat flux caused by the conductive heat transfer at the ‘contacting’ portions at the lower temperature. Even though the temperature is higher, the watt-density is uniform and, since the radiant and convective heat transfer are less efficient than conductive heat transfer, the ‘non-contacting’ portions must have a lower heat flux. Therefore, by controlling the ‘contacting’ portions to a safe temperature, for example, via a temperature sensor 121 coupled to heating element 10 in a location where element 10 will be in conductive contact with the body, as illustrated in FIG. 1D, the ‘non-contacting’ portions, for example, lateral portions 11, 12, will also be operating at a safe temperature because of the less efficient radiant and convective heat transfer. According to preferred embodiments, heating element 10 comprises a conductive fabric having a relatively small thermal mass so that when a portion of the heater that is operating at the higher temperature is touched, suddenly converting a ‘non-contacting’ portion into a ‘contacting’ portion, that portion will cool almost instantly to the lower operating temperature.

According to embodiments of the present invention, zones of heating element 10 may be differentiated according to whether or not portions of element 10 are in conductive contact with a body, for example, a patient undergoing surgery. In the case of conductive heating, gentle external pressure may be applied to a heating blanket including heating element 10, which pressure forces heating element 10 into better conductive contact with the patient to improve heat transfer. However, if excessive pressure is applied the blood flow to that skin may be reduced at the same time that the heat transfer is improved and this combination of heat and pressure to the skin can be dangerous. It is well known that patients with poor perfusion should not have prolonged contact with conductive heat in excess of approximately 42° C. 42° C. has been shown in several studies to be the highest skin temperature, which cannot cause thermal damage to normally perfused skin, even with prolonged exposure. (Stoll & Greene, Relationship between pain and tissue damage due to thermal radiation. J. Applied Physiology 14(3):373-382. 1959. and Moritz and Henriques, Studies of thermal injury: The relative importance of time and surface temperature in the causation of cutaneous burns. Am. J. Pathology 23:695-720, 1947) Thus, according to certain embodiments of the present invention, the portion of heating element 10 that is in conductive contact with the patient is controlled to approximately 43° C. in order to achieve a temperature of about 41-42° C. on a surface a heating blanket cover that surrounds element 10, for example, a cover or shell 20, 40 which will be described below in conjunction with FIGS. 3A and 4C. With further reference to FIG. 1D, flaps 125 are shown extending laterally from either side of heating element 10 in order to enclose the sides of body 16 thereby preventing heat loss; according to preferred embodiments of the present invention, flaps 125 are not heated and thus provide no thermal injury risk to body if they were to be tucked beneath sides of body 16.

Referring now to the end view of FIG. 1C, an alternate embodiment to that shown in FIG. 1B is presented. FIG. 1C illustrates subassembly 100 wherein insulating members 18, for example, fiberglass material strips having an optional PTFE coating and a thickness of approximately 0.003 inch, extend between bus bars 15 and heating element 10 at each stitched coupling 145, so that electrical contact points between bars 15 and heating element 10 are solely defined by the conductive thread of stitched couplings 145.

FIG. 2A is a top plan view of a heating element assembly 250, according to some embodiments of the present invention, which may be incorporated by blanket 200, which is shown in FIG. 3A and further described below. FIG. 2B is a section view through section line A-A of FIG. 2A. FIGS. 2A-B illustrate a temperature sensor assembly 421 assembled on side 14 of heater 10, and heater 10 overlaid on both sides 13, 14 with an electrically insulating layer 210, preferably formed of a flexible non-woven high loft fibrous material, for example, 1.5 OSY (ounces per square yard) nylon, which is preferably laminated to sides 13, 14 with a hotmelt laminating adhesive. In some embodiments, the adhesive is applied over the entire interfaces between layer 210 and heater 10. Other examples of suitable materials for layer 210 include, without limitation, polymeric foam, a woven fabric, a relatively thin plastic film, cotton, and a non-flammable material, such as fiberglass or treated cotton. According to preferred embodiments, overlaid layers 210, without compromising the flexibility of heating assembly 250, prevent electrical shorting of one portion of heater 10 with another portion of heater 10 if heater 10 is folded over onto itself. Because, according to preferred embodiments, heating element assembly 250 will be enclosed within a relatively durable and waterproof shell, for example shell 20 shown with dashed lines in FIG. 2B, and will be powered by a relatively low voltage (approximately 48V). Layers 210 may even be porous in nature to further maintain the desired flexibility of assembly 250.

FIG. 2C is an enlarged plan view and a corresponding end view schematic showing some details of the corner of assembly 250 that is circled in FIG. 2A, according to some embodiments. FIG. 2C is representative of each corner of assembly 250. FIG. 2C illustrates insulating layer 210 disposed over side 14 of heating element and extending beneath bus bar 15, optional electrical insulating member 18, and layer 210 disposed over side 13 of heater 10 and terminated adjacent bus bar 15 within lateral portion 12 so that threads of conductive stitching 145 securing bus bars 15 to heater 10 electrically contact heater 10 along side 13 of heater 10. FIG. 2C further illustrates two rows of conductive stitching 145 coupling bus bar 15 to heater 10, and bus bar 15 and insulating member 18 extending past end 102; a backtack securing stitching 145 may be approximately 0.375 inches long and also extends beyond end 102.

FIG. 2A further illustrates junctions 50 coupling leads 205 to each bus bar 15, and another lead 221 coupled to and extending from temperature sensor assembly 421; each of leads 205, 221 extend over insulating layer 210 and into an electrical connector housing 225 containing a connector 23, which will be described in greater detail below, in conjunction with FIGS. 3A-C. FIG. 2D is an enlarged view of junction 50, which is circled in FIG. 2A, according to some embodiments of the present invention. FIG. 2D illustrates junction 50 including a conductive insert 55 which has been secured to bus bar 15, for example, by inserting insert 55 through a side wall of bus bar 15 and into an inner diameter thereof, the bus bar 15 of the illustrated embodiment being formed by a braided wire tube so that an opening between the wires may be formed for access to the inner diameter. Insert 55 may be secured to bus bar 15 by compressing tubular bus bar 15 around insert 55 and further by stitching 145 that couples bus bar 15 to heating element 10. FIG. 2D further illustrates lead 205 coupled to insert 55, for example, via soldering, and an insulating tube and strain relief 54, for example, a polymer shrink tube, surrounding the coupling between lead 205 and insert 55.

Returning now to FIG. 2B, temperature sensor assembly 421 will be described in greater detail. FIG. 2B illustrates assembly 421 including a substrate 211, for example, of polyimide (Kapton), on which a temperature sensor 21, for example, a surface mount chip thermistor (such as a Panasonic ERT-J1VG103FA: 10K, 1% chip thermistor), is mounted; a heat spreader 212, for example, a copper or aluminum foil, is mounted to an opposite side of substrate 211. Temperature sensor assembly 421 may be bonded to layer 210 with an adhesive layer 213, for example, hotmelt EVA. Some alternate embodiments of the present invention address a non-uniform resistance across a surface area of element 10 by employing a distributed temperature sensor, for example, a resistance temperature detector (RTD) laid out in flat plane across a surface of heating element 10, or by employing an infrared temperature measurement device positioned to receive thermal radiation from a given area of heating element 10. An additional alternate embodiment is contemplated in which an array of temperature sensors are positioned over the surface of heating element 10, being spaced apart so as to collect temperature readings which may be averaged to account for resistance variance.

According to a preferred embodiment, assembly 421 includes a second, redundant, temperature sensor mounted to substrate 211, close enough to sensor 21 to detect approximately the same temperature; while sensor 21 may be coupled to a microprocessor temperature control, the second sensor, for example, a chip thermistor similar to sensor 21, may be coupled to an analog over-temperature cutout that cuts power to element 10, and/or sends a signal triggering an audible or visible alarm. The design of the second sensor may be the same as the first sensor and need not be described again. Another safety check may be provided by mounting an identification resistor to substrate 211 in order to detect an increase in resistance of element 10, due, for example, to degradation of the material of element 10, or a fractured bus bar; the optional identification resistor monitors a resistance of heating element 10 and compares the measured resistance to an original resistance of element 10.

According to some embodiments of the present invention, for example as illustrated in FIG. 2A, super over-temperature sensors 41 are incorporated to detect overheating of areas of assembly 250 susceptible to rucking, that is areas, for example, lateral portions 11, 12, where assembly 250 is most likely to be folded over on itself, either inadvertently or on purpose to gain access to a portion of a patient disposed beneath a blanket including assembly 250. An area of assembly 250 which is beneath the folded-over portion of assembly 250, and not in close proximity to sensor assembly 421, can become significantly warmer due to the additional thermal insulation provided by the folded-over portion that goes undetected by sensor 21. According to preferred embodiments, sensors 41 are wired in series, as illustrated in FIG. 2A. Super over-temperature sensors 41 may be set to open, or significantly increase resistance in, a circuit, for example, the over-temperature circuit, thereby activating an alarm and/or cutting power to heater 10, at prescribed temperatures that are significantly above the normal operating range, for example, temperatures between approximately 45° C. and approximately 60° C. Alternately, sensors 41 may be part of the bus bar power circuit, in which case sensors 41 directly shut down power to heater 10 when in an open condition or add sufficient resistance when in a high resistance condition to substantially reduce heating of heater 10.

FIG. 3A is a top plan view, including partial cut-away views, of a lower body heating blanket 200, according to some embodiments of the present invention, which may be used to keep a patient warm during surgery. FIG. 3A illustrates blanket 200 including heating element assembly 250 covered by flexible shell 20; shell 20 protects and isolates assembly 250 from an external environment of blanket 200 and may further protect a patient disposed beneath blanket 200 from electrical shock hazards. According to preferred embodiments of the present invention, shell 20 is waterproof to prevent fluids, for example, bodily fluids, IV fluids, or cleaning fluids, from contacting assembly 250, and may further include an anti-microbial element, for example, being a SILVERion™ antimicrobial fabric available from Domestic Fabrics Corporation. According to the illustrated embodiment, blanket 200 further includes a layer of thermal insulation 201 extending over a top side (corresponding to side 14 of heater 10) of assembly 250; layer 201 may or may not be bonded to a surface of assembly 250. Layer 201 may serve to prevent heat loss away from a body disposed on the opposite side of blanket 200, particularly if a heat sink comes into contact with the top side of blanket 200. FIG. 3C illustrates insulation 201 extending over an entire surface of side 14 of heater 10 and over sensor assembly 421. According to the illustrated embodiment, layer 201 is secured to heating element assembly 250 to form an assembly 250′, as will be described in greater detail below. According to an exemplary embodiment of the present invention, insulating layer 201 comprises a polymer foam, for example, a 1 pound density 30 ILD urethane foam, which has a thickness between approximately ⅛^(th) inch and approximately ¾^(th) inch. According to an alternate embodiment, layer 201 is formed of a high loft fibrous polymeric non-woven material.

FIG. 3A further illustrates shell 20 forming flaps 25 extending laterally from either side of assembly 250 and a foot drape 26 extending longitudinally from assembly 250. According to exemplary embodiments of the present invention, a length of assembly 250 is either approximately 28 inches or approximately 48 inches, the shorter length providing adequate coverage for smaller patients or a smaller portion of an average adult patient. FIG. 3B is a schematic side view of blanket 200 draped over a lower body portion of a patient. With reference to FIG. 3B it may be appreciated that flaps 25, extending down on either side of the patient, and foot drape 26, being folded under and secured by reversible fasteners 29 (FIG. 3A) to form a pocket about the feet of the patient, together effectively enclose the lower body portion of the patient to prevent heat loss. With further reference to FIG. 3B, it may also be appreciated that neither shell 20 nor insulation layer 201 add appreciable stiffness to heater 10 so that blanket 200 conforms nicely to the contour of the patient's lower body. With reference to FIG. 2A, in conjunction with FIG. 3B, it may be appreciated that temperature sensor assembly 421 is located on assembly 250 so that, when blanket 200 including assembly 250 is draped over the lower body of the patient, the area of heater 10 surrounding sensor assembly 421 will be in conductive contact with one of the legs of the patient in order to maintain a safe temperature distribution across heater 10.

According to some embodiments of the present invention, shell 20 includes top and bottom sheets extending over either side of assembly 250; the two sheets of shell 20 are coupled together along a seal zone 22 (shown with cross-hatching in the cut-away portion of FIG. 3A) that extends about a perimeter edge 2000 of blanket 200, and within perimeter edge 2000 to form zones, or pockets, where a gap exists between the two sheets. According to an exemplary embodiment of the present invention, shell 20 comprises a nylon fabric having an overlay of polyurethane coating to provide waterproofing; the coating is on at least an inner surface of each of the two sheets, further facilitating a heat seal between the two sheets, for example, along seal zone 22, according to preferred embodiments. It should be noted that, according to alternate embodiments of the present invention, a covering for heating assemblies, such as heating assembly 250, may be removable and, thus, include a reversible closure facilitating removal of a heating assembly therefrom and insertion of the same or another heating assembly therein.

FIG. 3A further illustrates flaps 25 including zones where there are gaps between the sheets to enclose weighting members, which are shown as relatively flat plastic slabs 255. Alternately flaps 25 can be weighted by attaching weighting members to exterior surfaces thereof. Examples of other suitable weighting members include but are not limited to a metal chain, a metal spring, lead shot, plastic rods and sand. The weighting of flaps 25 causes flaps 25 to hang down in order to provide a more secure air seal about the patient. The weighting members may further discourage a clinician from tucking flaps 25 under the patient as a safety feature to help to prevent a portion of the blanket containing heater 10 from coming into relatively high pressure contact with the patient, where it could cause serious burns; as such, the weighting members are relatively stiff and/or form a lump at the outer edge of flaps 25. Relatively stiff flap weighting members 255, for example, batten-like flat plastic slabs 255, by extending along the length of assembly 250, may further prevent inadvertent rucking of blanket 200, that is, the folding of blanket 200 over on itself, which could lead to over-heating of a portion of heater 10, as previously described. However, with reference to FIG. 3A, seal zone 22 extending between members 255 along each flap 25 can predetermine a folding location; the predetermined folding location can prevent overheating (due to the location of sensor assembly 421) or can dictate the placement of super over-temperature sensors 41, as previously described.

FIG. 3C is a top plan view, including partial cut-away views, of heating element assembly 250′, which may be incorporated in blanket 200; and FIG. 3D is a cross-section view through section line D-D of FIG. 3C. FIGS. 3C-D illustrates heating element assembly 250′ including heater 10 overlaid with electrical insulation 210 on both sides 13, 14 and thermal insulation layer 201 extending over the top side 14 thereof (dashed lines show leads and sensor assembly beneath layer 201). According to the illustrated embodiment, layer 201 is inserted beneath a portion of each insulating member 18, each which has been folded over the respective bus bar 15, for example as illustrated by arrow B in FIG. 1C, and then held in place by a respective row of non-conductive stitching 345 that extends through member 18, layer 201 and heater 10. Although not shown, it should be appreciated that layer 201 may further extend over bus bars 15. Although layer 210 is shown extending beneath layer 201 on side 14 of heating element, according to alternate embodiments, layer 201 independently performs as a thermal and electrical insulation so that layer 210 is not required on side 14 of heater 10. FIG. 3C further illustrates, with longitudinally extending dashed lines, a plurality of optional slits in layer 201, which may extend partially or completely through layer 201, in order to increase the flexibility of assembly 250′. Such slits are desirable if a thickness of layer 201 is such that it prevents blanket 200 from draping effectively about a patient; the optional slits are preferably formed, for example, extending only partially through layer 201 starting from an upper surface thereof, to allow bending of blanket 200 about a patient and to prevent bending of blanket 200 in the opposition direction.

Returning now to FIG. 2A, to be referenced in conjunction with FIGS. 3A-C, connector housing 225 and connector 23 will be described in greater detail. According to certain embodiments, housing 225 is an injection molded thermoplastic, for example, PVC, and may be coupled to assembly 250 by being stitched into place, over insulating layer 210. FIG. 2A shows housing 225 including a flange 253 through which such stitching can extend. With reference to FIGS. 3A-B, it can be seen that connector 23 protrudes from shell 20 of blanket 200 so that an extension cable 330 may couple bus bars 15 to a power source 234, and temperature sensor assembly 421 to a temperature controller 232, both shown incorporated into a console 333. In certain embodiments, power source 234 supplies a pulse-width-modulated voltage to bus bars 15. The controller 232 may function to interrupt such power supply (e.g., in an over-temperature condition) or to modify the duty cycle to control the heating element temperature. According to the illustrated embodiment, a surface 252 of flange 253 of housing 225 protrudes through a hole formed in thermal insulating layer 201 (FIG. 3C) so that a seal 202 (FIG. 3A) may be formed, for example, by adhesive bonding and/or heat sealing, between an inner surface of shell 20 and surface 252.

FIGS. 3C-D further illustrate a pair of securing strips 217, each extending laterally from and alongside respective lateral portions 11, 12 of heating element 10 and each coupled to side 13 of heating element 10 by the respective row of stitching 345. Another pair of securing strips 271 is shown in FIG. 3C, each strip 271 extending longitudinally from and alongside respective ends 101, 102 of heating element 10 and being coupled thereto by a respective row of non-conductive stitching 354. Strips 271 may extend over layer 201 or beneath heating element 10. Strips 217 preferably extend over conductive stitching 145 on side 13 of heating element 10, as shown, to provide a layer of insulation that can prevent shorting between portions of side 13 of heating element 10 if element 10 were to fold over on itself along rows of conductive stitching 145 that couple bus bars 15 to heating element 10; however, strips 217 may alternately extend over insulating member 18 on the opposite side of heating element 10. According to the illustrated embodiment, securing strips 217 and 271 are made of a polymer material, for example polyurethane, so that they may be heat sealed between the sheets of shell 20 in corresponding areas of heat seal zone 22 in order to secure heating element assembly 250′ within the corresponding gap between the two sheets of shell 20 (FIG. 3A).

FIG. 4A is a plan view of flexible heating element 30, according to some alternate embodiments of the present invention. Heating element 30 is similar in nature to previously described embodiments of heating element 10, being comprised of a conductive fabric, or a fabric incorporating closely spaced conductive elements, for a substantially uniform watt density output, preferably less than approximately 0.5 watts/sq. inch. While a shape of the surface area of heating element 10 is suited for a lower body blanket, such as blanket 200, that would cover a lower abdomen and legs of a patient (FIG. 3B) undergoing upper body surgery, the shape of a surface area of heating element 30 is suited for an upper body heating blanket, for example, blanket 300 shown in FIG. 4C, that would cover outstretched arms and a chest area of a patient undergoing lower body surgery (FIG. 4D). According to an exemplary embodiment for an adult upper body heating blanket, a distance between a first end 301 of element 30 and a second end 302 of element 30 is between about 70 and 80 inches, while a distance between a first lateral edge 311 and a second lateral edge 312 is about 7 to 10 inches. With reference to FIG. 4B, which shows heating element 30 incorporated into a heating element assembly 450, it can be seen that bus bars 15 are coupled to element 30 alongside respective lateral edges 311, 312 (FIG. 4A). For the narrower spacing between bus bars 15, compared with that for heating element 10 incorporated in blanket 200, element 30, in order to have the desired watt density output, should be comprised of a conductive fabric having a higher resistance than the examples previously recited for heating element 10, for example, on the order of 100 ohms per square, measured with a four point probe. An example of a conductive fabric meeting this resistance requirement is a woven silk-like polyester, for example, known as Pongee, being 100% coated with polypyrrole.

FIG. 4B is a top plan view, including partial cut-away views, of heating element assembly 450, according to some embodiments of the present invention, which may be incorporated in blanket 300 shown in FIG. 4C. FIG. 4B illustrates assembly 450 having a configuration similar to that of assembly 250′, which is illustrated in FIGS. 3C-D. According to the embodiment illustrated in FIG. 4B, temperature sensor assembly 421 is coupled to heating element 30 at a location where element 30, when incorporated in an upper body heating blanket, for example, blanket 300, would come into conductive contact with the chest of a patient, for example as illustrated in FIG. 4D, in order to maintain a safe temperature distribution across element 30; bus bar junctions 50 and connector housing 225 are located in proximity to sensor assembly 421 in order to keep a length of leads 205 and 221 to a minimum. With reference back to FIGS. 3C-D, in conjunction with FIG. 4B, an electrical insulating layer 310 of assembly 450 corresponds to insulating layers 210 of assembly 250′, a thermal insulating layer 301 of assembly 450 corresponds to layer 201 of assembly 250′, and securing strips 317 and 371 of assembly 450 generally correspond to strips 217 and 271, respectively, of assembly 250′.

FIG. 4C is a top plan view, including partial cut-away views, of upper body heating blanket 300, according to some embodiments of the present invention. FIG. 4C illustrates blanket 300 including heating element assembly 450 covered by a flexible shell 40; shell 40 protects and isolates assembly 450 from an external environment of blanket 300 and may further protect a patient disposed beneath blanket 300 from electrical shock hazards. According to preferred embodiments, shell 40 is similar to shell 20 of blanket 200 in that shell 40 is relatively durable and waterproof and may further include an antimicrobial element or layer extending over an exterior surface thereof. According to the illustrated embodiment, shell 40, like shell 20, includes top and bottom sheets; the sheets extend over either side of assembly 450 and are coupled together along a seal zone 32 that extends around a perimeter edge 4000 and within edge 4000 to form various zones, or pockets, where gaps exist between the two sheets. The sheets of shell 40 may be heat sealed together along zone 32, as previously described for the sheets of shell 20. With reference to FIG. 4B, securing strips 317 may be heat sealed between the sheets of shell 40 in corresponding areas of seal zone 32, on either side of a central narrowed portion 39 of blanket 300, in order to secure heating element assembly 450 within the corresponding gap between the two sheets of shell 40. According to an alternate embodiment, for example, as shown with dashed lines in FIG. 4A, lateral edges 311, 312 of heating element 30 extend out to form securing edges 27 that each include slots or holes 207 extending therethrough so that inner surfaces of sheets of shell 40 can contact one another to be sealed together and thereby hold edges 27. It should be noted that either of blankets 200, 300, according to alternate embodiments of the present invention, may include more than one heating element 10, 30 and more than one assembly 250/250′, 450.

With reference to FIG. 4C, it may be appreciated that blanket 300 is symmetrical about a central axis 30 and about another central axis, which is orthogonal to axis 30. FIG. 4C illustrates shell 40 forming flaps 35A, 35B and 350, each of which having a mirrored counterpart across central axis 30 and across the central axis orthogonal to axis 30. According to the illustrated embodiment, each of flaps 35A, B include weighting members 305, which are similar to members 255 of blanket 200, and which may stiffen flaps 35A,B (dashed lines indicate outlines of members 305 held between the sheets of cover 40 by surrounding areas of seal zone 32).

FIG. 4C further illustrates straps 38, each extending between respective flaps 35A-B. With reference to FIG. 4D, which is a schematic end view of blanket 300 draped over an upper body portion of a patient, it may be appreciated that flaps 35A-B and 350 extend downward to enclose the outstretched arms of the patient in order to prevent heat loss and that straps 38 secure blanket 300 about the patient. Opposing straps 38 may be secured together with reversible fasteners, examples of which include, without limitation, magnetic fasteners, either embedded within straps 38 or coupled to outer surfaces thereof, and mating hook-and-loop fasteners attached to opposing straps 38. According to preferred embodiments, portions of perimeter edge 4000 defining narrowed portion 39, which extends across a chest of the patient, are either rounded or padded to provide a softer interface with the patient's chin if blanket 300 were to slip off the patient's chest toward the patient's chin.

With further reference to FIG. 4D, it may also be appreciated that, when blanket 300 is positioned over the patient, each strap 38 is positioned in proximity to an elbow of the patient so that either end portion of blanket 300, corresponding to each pair of flaps 35A, may be temporarily folded back, as illustrated, per arrow C, in order for a clinician to access the patient's arm, for example, to insert or adjust an IV. According to some embodiments of the present invention, super over-temperature sensors, for example, sensors 41, previously described, are included in blanket 300 being located according to the anticipated folds, for example at general locations 410 illustrated in FIGS. 4B-C, in order to detect over-heating, which may occur if blanket 300 is folded over on itself, as illustrated in FIG. 4D, for too long a time, and, particularly, if flaps 35A of folded-back portion of blanket are allowed to extend downward as illustrated with the dashed line in FIG. 4D. FIG. 4D further illustrates connector cord 330 plugged into connector 23 to couple heating element 30 and temperature sensor assembly 421 of blanket 300 to control console 333.

In the foregoing detailed description, the invention has been described with reference to specific embodiments. However, it may be appreciated that various modifications and changes can be made without departing from the scope of the invention as set forth in the appended claims. Although embodiments of the invention are described in the context of a hospital operating room, it is contemplated that some embodiments of the invention may be used in other environments. Those embodiments of the present invention, which are not intended for use in an operating environment and need not meet stringent FDA requirements for repeated used in an operating environment, need not including particular features described herein, for example, related to precise temperature control. Thus, some of the features of preferred embodiments described herein are not necessarily included in preferred embodiments of the invention which are intended for alternative uses. 

1. An electric warming blanket, comprising: a flexible heater including a first side and a second side, at least one of the first and second sides having a surface area and a substantially uniform watt density output across the surface area when the element is electrically powered; a first layer of non-conductive flexible porous material bonded to the first side of the heater; a second layer of non-conductive flexible porous material bonded to the second side of the heater; and a first layer of water resistant material coupled to a second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater and the first and second non-conductive material layers bonded thereto.
 2. The blanket of claim 1, wherein the heater comprises carbon.
 3. The blanket of claim 1, wherein the heater comprises a nonconductive layer coated with a conductive material.
 4. The blanket of claim 3, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 5. The blanket of claim 3, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 6. The blanket of claim 3, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 7. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a woven fabric.
 8. The blanket of claim 7, wherein the woven fabric is formed of a non-flammable material.
 9. The blanket of claim 7, wherein the woven fabric is fiberglass or cotton.
 10. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a non-woven fabric.
 11. The blanket of claim 10, wherein the non-woven fabric comprises nylon or fiberglass.
 12. The blanket of claim 1, wherein each layer of non-conductive flexible porous material comprises a polymeric foam.
 13. The blanket of claim 1 wherein the first layer of water resistant material extends adjacent to the first layer of non-conductive flexible porous material and is un-adhered thereto.
 14. The blanket of claim 13, wherein the second layer of water resistant material extends adjacent to the second layer of non-conductive flexible porous material and is un-adhered thereto.
 15. The blanket of claim 1, further comprising: a first conductive bus bar coupled to the first side of the heater and extending alongside a first lateral edge of the heater; and a second conductive bus bar coupled to the first side of the heater and extending alongside a second lateral edge of the heater; wherein the first lateral edge is opposite the second lateral edge; the first and second bus bars are contained in the substantially hermetically sealed space formed by the first and second layers of water-resistant material; and the first and second bus bars are adapted for coupling to a power source for powering the heating element.
 16. The blanket of claim 15, wherein the first and second bus bars comprise a metal wire.
 17. The blanket of claim 16, wherein the metal wire is one of a plurality of braided metal wires.
 18. The blanket of claim 15, wherein the first and second bus bars comprise a metal foil.
 19. The blanket of claim 15, wherein the first and second bus bars comprise conductive ink.
 20. The blanket of claim 15, wherein the first and second bus bars are coupled to the heater by sewn threads.
 21. The blanket of claim 20, wherein the sewn threads are conductive.
 22. An electric warming blanket, comprising: a flexible heater including a first side and a second side, at least one of the first and second sides having a surface area and a substantially uniform watt density output across the surface area when the element is electrically powered; a first layer of water resistant material disposed over the first side of the heater, being un-adhered thereto, and forming an outer surface of the blanket when the blanket is draped over an object or a person to be warmed; a second layer of water resistant material disposed over the second side of the heater, being un-adhered thereto, and forming an inner surface of the blanket, adjacent to the object or the person, when the blanket is draped thereover; the first layer of water resistant material coupled to the second layer of water resistant material about a perimeter of the heater to form a substantially hermetically sealed space for the heater; and a layer of thermal insulation disposed between the first side of the heater and the first layer of water resistant material.
 23. The blanket of claim 22, wherein the heater comprises carbon.
 24. The blanket of claim 22, wherein the heater comprises a nonconductive layer coated with a conductive material.
 25. The blanket of claim 24, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 26. The blanket of claim 24, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 27. The blanket of claim 24, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 28. The blanket of claim 22, wherein the layer of thermal insulation comprises a flexible polymeric foam.
 29. The blanket of claim 22, wherein the layer of thermal insulation includes a plurality substantially parallel slits extending partially therethrough.
 30. The blanket of claim 22, wherein the layer of thermal insulation includes a plurality of substantially parallel slits extending completely therethrough.
 31. The blanket of claim 22, wherein the layer of thermal insulation comprises a high loft fibrous polymeric non-woven material.
 32. The blanket of claim 22, wherein the layer of thermal insulation is attached to the heater.
 33. The blanket of claim 22, wherein the layer of thermal insulation is un-attached to the heater.
 34. The blanket of claim 22, further comprising: a first conductive bus bar coupled to the first side of the heater and extending alongside a first lateral edge of the heater; and a second conductive bus bar coupled to the first side of the heater and extending alongside a second lateral edge of the heater; wherein the first lateral edge is opposite the second lateral edge; the first and second bus bars are contained in the substantially hermetically sealed space formed by the first and second layers of water-resistant material; the first and second bus bars are adapted for coupling to a power source for powering the heating element; and the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink.
 35. The blanket of claim 34, wherein the layer of thermal insulation extends over the first and second bus bars.
 36. An electric warming blanket, comprising: a flexible heater including a first lateral edge and a second lateral edge opposite the first lateral edge; a flexible shell enveloping the flexible heater, to form a substantially hermetically sealed space for the flexible heater, and extending beyond both the first and second lateral edges of the heater; at least one first stiffening member supported by the flexible shell beyond the first lateral edge of the heater; and at least one second stiffening member supported by the flexible shell beyond the second lateral edges of the heater.
 37. The blanket of claim 36, wherein the flexible heater comprises a conductive fabric.
 38. The blanket of claim 36, wherein the flexible heater comprises carbon.
 39. The blanket of claim 36, wherein the flexible heater comprises a nonconductive layer coated with a conductive material.
 40. The blanket of claim 39, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 41. The blanket of claim 39, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 42. The blanket of claim 39, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 43. The blanket of claim 36, wherein each of the at least one first and the at least one second stiffening members comprise a polymeric material.
 44. The blanket of claim 36, wherein each of the at least one first and the at least one second stiffening members extend along a length of the heater.
 45. The blanket of claim 44, wherein each of the at least one first and the at least one second stiffening members comprise a pair of stiffening members.
 46. The blanket of claim 45, wherein each pair of more than one pair of stiffening members is separated by a flexible gap along the length of the heater.
 47. The blanket of claim 36, wherein the flexible shell comprises a first layer of water resistant material coupled to a second layer of water resistant material about a perimeter of the heater and about at least a portion of a perimeter of each of the at least one first stiffening member and the at least one second stiffening member.
 48. The blanket of claim 36, further comprising: a first conductive bus bar coupled to the heater and extending alongside the first lateral edge of the heater; and a second conductive bus bar coupled to the heater and extending alongside a second lateral edge of the heater; wherein the first and second bus bars are contained in the substantially hermetically sealed space formed by the flexible shell; the first and second bus bars are adapted for coupling to a power source for powering the heater; and the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink.
 49. An electric warming blanket, comprising: a flexible heater including a first lateral edge and a second lateral edge opposite the first lateral edge; a first conductive bus bar coupled to the heater and extending alongside the first lateral edge of the heater; a second conductive bus bar coupled to the heater and extending alongside the second lateral edge of the heater; a temperature sensor coupled to the heater at a location between the first and second bus bars where the heater will be in conductive contact with a body when the blanket is draped over the body; the temperature sensor providing input to a temperature controller, the controller adapted to control a supply of power to the first and second bus bars, the supply of power being based on a sensed temperature from the temperature sensor; and at least one super over-temperature sensor coupled to the heater between the first and second bus bars; the at least one super over-temperature sensor adapted to interrupt the supply of power to the first and second bus bars when a temperature sensed by the at least one super over-temperature sensor exceeds a prescribed temperature.
 50. The blanket of claim 49, further comprising an over-temperature sensor coupled to the heater in proximity to the temperature sensor, the over-temperature sensor providing redundant input to the temperature controller.
 51. The blanket of claim 49, further comprising a flexible shell enveloping the flexible heater, to form a substantially hermetically sealed space for the flexible heater, the first and second bus bars, the temperature sensor and the at least one super-over temperature sensor.
 52. The blanket of claim 49, wherein the at least one super-over temperature sensor comprises a plurality of super over-temperature sensors wired in series with one another.
 53. The blanket of claim 52, wherein a first portion of the plurality of super over-temperature sensors is disposed in proximity to the first bus bar and a second portion of the plurality of super over-temperature sensors is disposed in proximity to the second bus bar.
 54. The blanket of claim 49, wherein the at least one super-over temperature sensor is disposed in proximity to one of the first and second bus bars.
 55. The blanket of claim 49, wherein the heater comprises carbon.
 56. The blanket of claim 49, wherein the heater comprises a nonconductive layer coated with a conductive material.
 57. The blanket of claim 56, wherein the nonconductive layer of the heater comprises a woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 58. The blanket of claim 56, wherein the nonconductive layer of the heater comprises a non-woven polymer and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 59. The blanket of claim 56, wherein the non-conductive layer of the heater comprises a non-woven cellulose material and the conductive material comprises one of: polypyrrole, carbonized ink and metalized ink.
 60. The blanket of claim 49, wherein the at least one super over-temperature sensor interrupts the supply of power by opening a power circuit that couples the supply of power to the first and second bus bars.
 61. The blanket of claim 49, wherein the at least one super over-temperature sensor interrupts the supply of power by increasing in resistance.
 62. The blanket of claim 49, wherein the at least one super over-temperature sensor is part of an over-temperature circuit adapted to indirectly interrupt the supply of power.
 63. The blanket of claim 49, wherein the at least one super over-temperature sensor is part of a power circuit which is adapted to directly interrupt the supply of power.
 64. The blanket of claim 49, wherein the prescribed temperature is in a range from approximately 45° C. to approximately 60° C.
 65. The blanket of claim 49, wherein the first and second bus bars comprise one of: a metal wire, a metal foil and a conductive ink. 